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Development of a nanoindenter for in-situ transmission electron microscopy (open access)

Development of a nanoindenter for in-situ transmission electron microscopy

In-situ transmission electron microscopy is an established experimental technique that permits direct observation of the dynamics and mechanisms of dislocation motion and deformation behavior. In this paper, we detail the development of a novel specimen goniometer that allows real time observations of the mechanical response of materials to indentation loads. The technology of the scanning tunneling microscope is adopted to allow nanometer scale positioning of a sharp, conductive diamond tip onto the edge of an electron transparent sample. This allows application of loads to nanometer-scale material volumes couple with simultaneous imaging of the material response. The emphasis in this paper is experimental and descriptive, with particular attention given to sample geometry and other technical requirements. Examples of the deformation of aluminum and titanium carbide as well as the fracture of silicon will be presented.
Date: January 30, 2001
Creator: Stach, Eric A.; Freeman, Tony; Minor, Andrew M.; Owen, Doug K.; Cumings, John; Wall, Mark A. et al.
System: The UNT Digital Library
Growth of Laser Initiated Damage in Fused Silica at 351 nm (open access)

Growth of Laser Initiated Damage in Fused Silica at 351 nm

The lifetime of optics in high-fluence UV laser applications is typically limited by the initiation of damage and its subsequent growth. We have measured the growth rate of laser-induced damage on fused silica surfaces in both air and vacuum. The data shows exponential growth in the lateral size of the damage site with shot number above a threshold fluence. The concurrent growth in depth follows a linear dependence with shot number. The size of the initial damage influences the threshold for growth; the morphology of the initial site depends strongly on the initiating fluence. We have found only a weak dependence on pulse length for growth rate. Most of the work has been on bare substrates but the presence of a sol-gel AR coating has no significant effect.
Date: January 30, 2001
Creator: Norton, M A; Hrubesh, L W; Wu, Z; Donohue, E E; Feit, M D; Kozlowski, M R et al.
System: The UNT Digital Library
The origins of quark-hadron duality: How does the square of the sum become the sum of the squares? (open access)

The origins of quark-hadron duality: How does the square of the sum become the sum of the squares?

Bloom-Gilman duality demonstrates empirically that the electroproduction of N*'s at low momentum transfers averages smoothly around the scaling curve measured at large momentum transfers. The latter is proportional to the sum of the squares of the constituent charges whereas the former involves the coherent excitation of resonances and is driven by the square of summed constituent charges. We determine the minimal necessary conditions for this equality to be realized so that duality can occur and consider the implications for a range of processes that may be studied soon at CEBAF.
Date: January 30, 2001
Creator: Close, Frank E. & Isgur, Nathan
System: The UNT Digital Library
Thermal Performance Analysis of a High-Mass Residential Building (open access)

Thermal Performance Analysis of a High-Mass Residential Building

Minimizing energy consumption in residential buildings using passive solar strategies almost always calls for the efficient use of massive building materials combined with solar gain control and adequate insulation. Using computerized simulation tools to understand the interactions among all the elements facilitates designing low-energy houses. Finally, the design team must feel confident that these tools are providing realistic results. The design team for the residential building described in this paper relied on computerized design tools to determine building envelope features that would maximize the energy performance [1]. Orientation, overhang dimensions, insulation amounts, window characteristics and other strategies were analyzed to optimize performance in the Pueblo, Colorado, climate. After construction, the actual performance of the house was monitored using both short-term and long-term monitoring approaches to verify the simulation results and document performance. Calibrated computer simulations showed that this house consumes 56% less energy than would a similar theoretical house constructed to meet the minimum residential energy code requirements. This paper discusses this high-mass house and compares the expected energy performance, based on the computer simulations, versus actual energy performance.
Date: January 30, 2001
Creator: Smith, M. W.; Torcellini, P. A.; Hayter, S. J. & Judkoff, R.
System: The UNT Digital Library
Electroweak and B physics results from the Fermilab Tevatron Collider (open access)

Electroweak and B physics results from the Fermilab Tevatron Collider

This writeup is an introduction to some of the experimental issues involved in performing electroweak and b physics measurements at the Fermilab Tevatron. In the electroweak sector, we discuss W and Z boson cross section measurements as well as the measurement of the mass of the W boson. For b physics, we discuss measurements of B{sup 0}/{bar B}{sup 0} mixing and CP violation. This paper is geared towards nonexperts who are interested in understanding some of the issues and motivations for these measurements and how the measurements are carried out.
Date: January 30, 2001
Creator: Pitts, K.T.
System: The UNT Digital Library
Radial and elliptic flow at RHIC: Further predictions (open access)

Radial and elliptic flow at RHIC: Further predictions

Using a hydrodynamic model, we predict the transverse momentum dependence of the spectra and the elliptic flow for different hadrons in Au+Au collisions at sqrt(s)=130 AGeV. The dependence of the differential and p{_}t-integrated elliptic flow on the hadron mass, equation of state and freeze-out temperature is studied both numerically and analytically.
Date: January 30, 2001
Creator: Huovinen, Pasi; Kolb, Peter F.; Heinz, Ulrich; Ruuskanen, P.V. & Voloshin, Sergei A.
System: The UNT Digital Library
Heavy flavor production in hadronic collisions (open access)

Heavy flavor production in hadronic collisions

None
Date: January 30, 2001
Creator: Bedeschi, F.
System: The UNT Digital Library
Local and average crystal structure and displacements of La{sup 11}B{sub 6} and EuB{sub 6} as a function of temperature (open access)

Local and average crystal structure and displacements of La{sup 11}B{sub 6} and EuB{sub 6} as a function of temperature

Measurements of both the average crystal structure from Rietveld refinement of neutron powder diffraction (NPD) data and the local structure from La L{sub III}-edge x-ray-absorption fine-structure (XAFS) are presented for a La{sup 11}B{sub 6} sample as a function of temperature ({approx}10-320 K). These data are compared to XAFS results on a EuB{sub 6} sample. The single-site La and B positional distribution widths and the La-B and La-La bond length distribution widths and their temperature dependence are compared. This comparison allows an estimate of the La and B site displacements, and we find that these sublattices are only slightly correlated with each other. Moreover, while the temperature dependence of the displacement parameters of the average sites from diffraction fit an Einstein model well, the temperature dependence of the La-B bond length distribution width requires at least two vibrational frequencies, corresponding to the La and B frequencies of the individual sites. XAFS data on EuB{sub 6} indicate that the situation is the same in the Eu compound. In addition, comparisons between data taken below and above the ferromagnetic transition temperature for EuB{sub 6} place stringent limits on the lattice involvement in the associated metal-insulator transition and the ensuing large magnetoresistance effect. This …
Date: January 30, 2001
Creator: Booth, C. H.; Sarrao, J. L.; Hundley, M. F.; Cornelius, A. L.; Kwei, G. H.; Bianchi, A. et al.
System: The UNT Digital Library